Final answer:
The biological macromolecule that is least soluble in water is a lipid, which is nonpolar and hence hydrophobic, unlike the more soluble polar macromolecules such as proteins, carbohydrates, and nucleic acids.
Step-by-step explanation:
The biological macromolecule that is least soluble in water is a lipid. Lipids are comprised of oils, fats, and waxes which are hydrophobic, meaning they do not mix well with water. In contrast, other biological macromolecules like carbohydrates, proteins, and nucleic acids are more soluble in water due to their polar characteristics which allow them to form hydrogen bonds with water molecules. Lipids, unlike these other macromolecules, are generally nonpolar and therefore do not have an affinity for water.
Macromolecules
Proteins, carbohydrates, nucleic acids, and lipids are the four major classes of biological macromolecules. These are essential for life and are made up of smaller organic molecules known as monomers. Through dehydration synthesis, where water is removed, these monomers join together to form larger polymers with diverse functions within the cell.